The invention relates to the new and distinct Hibiscus plant ‘15516 GR’. ‘15516 GR’ was generated from a cross performed on Jun. 22, 2014 near Vernon, Tex. between ‘11490-5’ (pod parent, unpatented) and ‘13028-2’ (pollen parent, unpatented). The pedigrees of each parent reflect a complex mixture of Hibiscus species. The pedigree of the pod parent includes H. mocheutos and H. coccineus. The pedigree of the pollen parent includes H. mocheutos, H. coccineus, H. militaris, and H. dasycalyx. The seed from this cross was harvested on Jul. 30, 2014 and the ‘15516 GR’ seedling was selected in the summer of 2015. ‘15516 GR’ was first asexually propagated near Vernon, Tex. in 2016 by stem tip cuttings. The resulting as well as subsequent asexually propagated plants have been stable and true to type throughout successive generations.